Acute effects of combined cycling and plyometrics on vertical jump performance in active males

The aim of this study was to analyze the acute effects of high vs low-intensity cycling efforts, combined with plyometrics, on vertical jump performance. Twenty-four physically active men (mean ± SD: 23 ± 2 years, 72.1 ± 10.1 kg, 1.73 ± 0.07 m) were randomly divided into two groups: experimental group (EXP, n = 16) and control group (CON, n = 8). EXP competed 2 experimental trials in a random order: (a) short high-intensity interval exercise (HI + Plyo) [5 × 10 s of cycling (“all-out”)/50 s active rest] or (b) low-intensity continuous exercise (LO + Plyo) [5 min of cycling at 75% of the HRmax)], along with 3 × 10 plyometric bounds (drop jumps)/1 min rest between sets. CON used a preconditioning activity of 13 min of low intensity cycling at ~60% of HRmax. Both EXP interventions significantly increased (p ≤ 0.05) the countermovement jump (CMJ) height at 1 min, 3 min, 6 min and 9 min compared to baseline, while the CON remained unchanged. There were no significant differences in CMJ performance enhancement between HI + Plyo (largest 11.2% at 9 min) and LO + Plyo (largest 15.0% at 3 min) at any time-point, suggesting that the plyometric component may be most important, with HR recovery taking slightly longer following HI + Plyo. The findings suggest that CMJ performance can be enhanced following high or low-intensity cycling combined with plyometric preconditioning activities in active males, the optimum recovery period likely to be individual-specific.


INTRODUCTION
The ability to develop muscular power (energy output per unit of time) is critical to successful outcomes in many sports events, such as sprint races, long and high jumps and other sporting actions like swimming starts or accelerations during team-based sports [1]. Some activities or actions (e.g., sprint, heavy-load exercises or stretching) performed before sport (warm-up) have shown acute improvements in subsequent performance [2,3]. A proposed mechanism underpinning such acute performance enhancement is post-activation potentiation (PAP). Several authors have demonstrated that muscle PAP is a phenomenon that can acutely increase muscular power and, consequently, performance [4,5]. PAP might cause gains in power after heavy muscle preloading as a result of myosin light chain phosphorylation and increased recruitment of higher order motor units [6]. However, the efficacy of PAP mechanisms to enhance performance ultimately depends on the balance between competing and simultaneous fatigue and PAP phenomena [6]. This balance is affected by many factors, including training experience of the athletes [4,7], recovery period [8] and the intensity of the conditioning activity performed [9].

Acute effects of combined cycling and plyometrics on vertical jump performance in active males
on vertical jump performance and heart rate (HR) compared to a control condition. EXP competed 2 experimental trials, (a) HI + PLYO -short high-intensity interval exercise [5 × 10 s of cycling ("allout")/50 s active rest] or (b) LO + PLYO -low-intensity continuous exercise [5  1) all subjects were familiarized with the countermovement jump (CMJ) and before each warm-up condition, three maximal CMJ were performed; 2) the warm-up conditions were randomized; 3) time of day, diet, hydration, and physical activity performed and use of caffeine were controlled in the days prior to testing. Subjects refrained from caffeine use before each training session.
Then, a CMJ was performed on a force platform Kistler Quattro-Jump (Kistler, Switzerland) at 500 Hz considered as the gold investigate the optimal recovery time for these athletes according to the preconditioning activity.
Therefore, the main aim of this study was to analyze the acute effects of high vs low-intensity cycling efforts, combined with plyometrics, on markers of vertical jump performance and heart rate.
The second aim was to analyze the influence of recovery time poststimulus. We hypothesized that the combination of cycling with plyometrics would enhance jump performance compared to a control condition, but with a differing time-course of PAPE effects for highintensity vs. low-intensity cycling conditions.

Subjects
Twenty-four physically active men (mean ± SD: 23 ± 2 years, 72.1 ± 10.1 kg, 1.73 ± 0.07 m) participated in this study. Subjects were non-smokers, free from any pre-existing medical conditions and musculoskeletal injuries. They performed varied sporting activities ("gym"-based training, endurance exercises such as running and swimming, and various sports such as soccer and basketball), habitually exercising for > 6 h per week.

Experimental design
A randomized and crossover study design was used to compare the effects of cycling efforts (high vs low-intensity) along with plyometrics Acute effects of combined cycling and plyometrics on jump standard that served as baseline [24]. The force platform was calibrated according to the manufacturer's recommendations. The order of EXP conditions for each subject was determined by block randomization using an online randomization tool. After baseline CMJ, all groups performed the preconditioning activities after a standardized 5 min of cycling at 60% HR max . Finally, CMJ and HR were measured at 1 min, 3 min, 6 min and 9 min of rest ( Figure 1) to profile both transient fatigue and potentiation effects. Before the CMJ assessment, the subjects stood motionless on the force platform to measure their body weight [25]. Participants were instructed to perform each vertical jump "as high as possible", with both hands placed on the hip followed by a rapid decent to a self-determined squat depth. CMJ performance variables assessed were jump height (cm), relative maximal force (%BW), average power (Watts), average force (N) and average velocity (m/s) of the CMJ were recorded from a force plate. The selected variables have been described as used to assess explosive leg muscle function [26]. These variables were automatically calculated through take-off velocity using MARS software (Kistler, Winterthur, Switzerland).
The HI and LO cycling were performed on the same cycle ergometer (Technogym, Gambettola, Italy) and the plyometrics jumps from the same box of 40 cm height (Technogym, Gambettola, Italy). Finally, HR was measured continuously during the preconditioning activities and recovery periods using a Polar® watch (Vantage M, Polar, Kempele, Finland) and a heart rate sensor with a chest band (H10 sensor, Polar, Kempele, Finland). The overview of experimental design is shown in Figure 1.

Statistical analysis
Statistical analyses were performed using SPSS software (version 21; SPSS, Inc, Chicago, IL, USA). Data are presented as mean ± SD.
Significance was set at p ≤ 0.05. Data were screened for normality of distribution and homogeneity of variance using a Shapiro-Wilk Normality Test. Two-way (3 × 5) mixed analyses of variance (betweengroups factors: condition [HI + Plyo, LO + Plyo, CON] × time [within-groups factors: baseline, 1 min, 3 min, 6 min and 9 min]) were used. Mauchly's test was consulted and if sphericity was violated, Greenhouse-Geisser correction was applied. Post-hoc Bonferroni adjustment was applied for post-hoc pairwise comparisons. We calculated the effect size using the partial eta squared (ŋ 2 ). Values of 0.01, 0.06 and above 0.15 were considered as small, medium, and large, respectively [27].

RESULTS
The results for the CMJ parameters are displayed at the Table 1. (p ≤ 0.01) at 1 min, 3 min, 6 min and 9 min compared to baseline. Furthermore, following 1 min of recovery, HRs were significantly (p ≤ 0.05) lower in CON compared to HI + PLYO, LO + PLYO and CON. Following 6 min of recovery HRs were also significantly lower in CON than HI + PLYO (p ≤ 0.05), with no further significant differences between conditions at other time-points ( Figure 3).

DISCUSSION
The main findings of the present study indicate that combined cycling and plyometric activity acutely enhances CMJ height in recreationally active males between 1 min and 9 min post-stimulus, compared to no significant effect of a lower intensity cycling control condition.
However, there was no evidence that one experimental condition was superior over the other, suggesting that the plyometric aspect may be the crucial component. The only slight difference between experimental conditions was that HR remained elevated 6 min poststimulus following the higher intensity cycling intervention. It is noted that there were no differences in how elevated HR (vs. CON) was between HI + Plyo and LO + Plyo 1 min post-stimulus, again suggesting the plyometric aspect may have been predominant in dictating the intensity of the conditioning stimulus.
There is good evidence of a performance-enhancing effect from the preconditioning activities, and this could in part be due to an  Data are presented as mean ± standard deviation.
CMJ countermovement jump, HI short high intensity interval exercise, LO low intensity continuous exercise, CON control condition, Plyo Plyometrics, RMF relative maximal force, %BW % body weight, W watts, bracket = all conditions different from baseline, * p < 0.05; ** p < 0.01; *** p < 0.001. Acute effects of combined cycling and plyometrics on jump increase in the peak force and rate of force development of a twitch contraction [28,29], mainly due to an increase in calcium sensitivity of the acto-myosin complex caused by phosphorylation of the my- to the outcome measure (vertical CMJ), as has been highlighted in more trained participants [13]. For that reason, we consider that the plyometric aspect may be the crucial component due to the specificity of preconditioning activity with the outcome measure (CMJ).
A previous meta-analysis and systematic review about PAP [4] showed that conditioning activity augmented power output, and these effects increased with training experience. In addition, potentiation was optimal following multiple sets at moderate intensities (60-85% 1RM) and using recovery period lengths between 7-10 min. Previous studies have shown a 4 min recovery duration was better than 5 min compared to baseline vertical jump height [31]. However, as we have observed in our study, a consistent optimal time did not seem to depend on the intensity of previous cycling effort, with similar cardiovascular stress between experimental conditions ( Figure 2).  [35]. Given that our participants are not high-performance athletes performing CMJs as part of daily monitoring for example, although CMJ height data was consistent (e.g., CON trial data), changes in CMJ technique are likely to have occurred jump-to-jump, resulting in variations in force, velocity and power variables. A further contributing factor is likely that of individual differences, as has been reported extensively in PAP literature [23]. For example, in the HI + Plyo condition, 37.5% of the subjects achieved the higher CMJ height at 1 min, 6.25% at 3 min, 31.25% at 6 min and 25% at 9 min post conditioning activity. However, in the case of the LO + Plyo condition, 25% of the subjects achieved the higher CMJ height at 1 min, 37.5% at 3 min, and 18.75% at both 6 min and 9 min post conditioning activity. Therefore, coaches and athletes must evaluate the individual effect of PAP to achieve the best jump performance. As demonstrated here again, there is high variability between subjects in terms of the optimal recovery time. More studies are needed to analyze the causes of these differences, and therefore, the results must be considered at the individual level. Finally, our results can be applied to physically active men, as women were not included in our study due to the convenience sampling employed.

CONCLUSIONS
In conclusion, this study has shown that up to 15% CMJ performance enhancement can be elicited following high or low-intensity cycling combined with plyometric preconditioning activities in active males, with the intensity and movement specificity of the plyometric component likely the crucial component. Our results suggest that the optimal recovery time within the 1 min-9 min window may be individualized.

Practical applications
From a practical viewpoint, we recommended that coaches use combined cycling efforts (high and low-intensity) and drop jumps to acutely improve subsequent CMJ performance. Coaches may wish to explore if there is a consistent optimal recovery time on an individual basis.

Conflict of interest declaration
The authors declare no conflict of interest.